This invention relates to a pressure regulator and safety valve assembly.
A great many varieties of fluid pressure regulators are known and these are used in a wide variety of applications to adjust the pressure within a contained volume. Usually it is necessary to provide a safety valve to ensure that the pressure in the contained volume does not exceed a predetermined limit. Such an excess pressure can be developed if, for example, the pressure regulating mechanism sticks. Without a safety valve this could lead to an increase of pressure within the contained volume to a level at which the boundary walls defining the contained volume are likely to fail. Thus it is common practice to fit a safety valve on a boundary wall of the contained volume with the safety valve set to open at a predetermined pressure above the normal working pressure but below the pressure at which the boundary walls of the contained volume could fail.
This arrangement is reasonably satisfactory provided the working pressure of the contained volume remains constant and provided the maximum safe pressure in the contained volume remains constant. However, there are situations where the working pressure varies widely according to the use to which the apparatus is to be put and also where the maximum safe pressure varies widely. In this case, it is possible that for a first use there is a low working pressure and a low maximum safe pressure and for a second use there is a high working pressure and a high maximum safe pressure. In order to prevent false opening of the safety valve in the second use, the safety valve must be arranged to open above the high working pressure of the second use, but this pressure may be greater than the maximum safe pressure of the first use, so that the safety valve is ineffective in this first use.
In order to overcome this problem it has been proposed to provide a pressure regulator including a safety valve arranged such that the pressure at which the safety valve opens varies in dependence upon the setting of the pressure regulating means. An example of such a regulator is described in British Patent Specification No. 1,511,844 in the name of Francis Xavier Kay.
In such a regulator the working pressure is controlled by movement of a piston acted upon on one side by a compression spring and on the other side by the pressurized gas. The regulated pressure is adjusted by altering the compression in the spring. The piston has a central aperture normally closed by a safety valve member but, in the event of excess pressure developing, the piston moves towards the spring adding to the compression in the spring and this movement of the piston causes relative movement of the piston and the safety valve member such that the central aperture in the piston is vented.
With such a regulator, however, one possible cause of the development of excess pressure is the sticking of the piston. In this case the piston will not move and consequently there is no relative movement of the piston and safety valve member and the safety valve remains closed. This is a serious disadvantage.